High-temperature superconducting materials based on the Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.z or 123 formulation (z having a value substantially higher than 6 but lower than 7) have been known to have a superconducting transition temperature (T.degree.) of approximately 90.degree. K. (Wu et al, Physical Review Letters, Vol. 58, pp. 908-910, 1987).
In addition to a high T.sub.c, it is desirable for a superconducting material to have a high diamagnetic susceptibility (x), high magnetization at low magnetic fields (M.sub.max) and high remanent magnetic hysteresis at higher magnetic fields (delta M). Such properties make a material suitable for applications involving levitation based on the Meissner effects, such as the production of frictionless bearings. Furthermore, such properties are indicative of a high critical current (J.sub.c), which is important for electronic applications.
It is known that the method of preparation of bulk superconducting materials has a significant effect on the properties of these materials. For example, materials prepared by sintering mixed oxide powders of the stoichiometric 123 composition below or around its incongruent melting point, i.e. below about 1000.degree. C., are known to provide low values of x, M.sub.max and delta M. This is especially true for bulk materials, as distinguished from wires or films.
In the production of high Tc Y-Ba-Cu-O superconductors, the ratio Y:Ba:Cu of 1:2:3 has been considered optimum in order to provide single crystal superconductors and thin film semiconductors with the best properties. In general, deviations from this ratio, as well as the substitution of other rare earths for yttrium, do not improve the magnetic and electrical properties of the superconductors, and in fact generally tend to diminish the magnetic and electrical properties of the superconductor.
It has been unexpectedly found in the present invention that when 123 based superconducting materials are prepared by heating the mixed oxides in a one or two step melt process, a substantial enrichment of the 123 composition with respect to yttrium content or addition of further Group III or Group V metal can result in significantly improved magnetic and electric properties.